/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package ai.platon.pulsar.filter;

import ai.platon.pulsar.common.config.ImmutableConfig;
import ai.platon.pulsar.crawl.filter.UrlFilter;

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * <p>
 * Validates URLs.
 * </p>
 * <p>
 * <p>
 * Originally based in on php script by Debbie Dyer, validation.php v1.2b, Date:
 * 03/07/02, http://javascript.internet.com. However, this validation now bears
 * little resemblance to the php original.
 * </p>
 * <p>
 * <pre>
 *   Example of usage:
 *    UrlValidator urlValidator = UrlValidator.get();
 *    if (urlValidator.isValid("ftp://foo.bar.com/")) {
 *       System.out.println("url is valid");
 *    } else {
 *       System.out.println("url is invalid");
 *    }
 *
 *   prints out "url is valid"
 * </pre>
 * <p>
 * <p>
 * Based on UrlValidator code from Apache commons-validator.
 * </p>
 *
 * @see <a href='http://www.ietf.org/rfc/rfc2396.txt' > Uniform Resource
 * Identifiers (URI): Generic Syntax </a>
 */
public class UrlValidator implements UrlFilter {

    public static final String ALPHA_CHARS = "a-zA-Z";
    public static final String ALPHA_NUMERIC_CHARS = ALPHA_CHARS + "\\d";
    public static final String SPECIAL_CHARS = ";/@&=,.?:+$";
    public static final String VALID_CHARS = "[^\\s" + SPECIAL_CHARS + "]";
    public static final String SCHEME_CHARS = ALPHA_CHARS;
    // Drop numeric, and "+-." for now
    public static final String AUTHORITY_CHARS = ALPHA_NUMERIC_CHARS + "\\-\\.";
    public static final String ATOM = VALID_CHARS + '+';
    /**
     * This expression derived/taken from the BNF for URI (RFC2396).
     */
    public static final Pattern URL_PATTERN = Pattern
            .compile("^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\\?([^#]*))?(#(.*))?");
    /**
     * Schema/Protocol (ie. http:, ftp:, file:, etc).
     */
    public static final int PARSE_URL_SCHEME = 2;

    /**
     * Includes hostname/ip and port number.
     */
    public static final int PARSE_URL_AUTHORITY = 4;
    public static final int PARSE_URL_PATH = 5;
    public static final int PARSE_URL_QUERY = 7;

    /**
     * Protocol (ie. http:, ftp:,https:).
     */
    public static final Pattern SCHEME_PATTERN = Pattern.compile("^["
            + SCHEME_CHARS + "]+");
    public static final Pattern AUTHORITY_PATTERN = Pattern.compile("^(["
            + AUTHORITY_CHARS + "]*)(:\\d*)?(.*)?");
    public static final int PARSE_AUTHORITY_HOST_IP = 1;
    public static final int PARSE_AUTHORITY_PORT = 2;
    public static final int PARSE_AUTHORITY_EXTRA = 3;

    public static final Pattern PATH_PATTERN = Pattern.compile("^(/[-\\w:@&?=+,.!/~*'%$_;\\(\\)]*)?$");
    public static final Pattern QUERY_PATTERN = Pattern.compile("^(.*)$");
    public static final Pattern LEGAL_ASCII_PATTERN = Pattern.compile("^[\\x21-\\x7E]+$");
    public static final Pattern IP_V4_DOMAIN_PATTERN = Pattern.compile("^(\\d{1,3})[.](\\d{1,3})[.](\\d{1,3})[.](\\d{1,3})$");
    public static final Pattern DOMAIN_PATTERN = Pattern.compile("^" + ATOM + "(\\." + ATOM + ")*$");
    public static final Pattern PORT_PATTERN = Pattern.compile("^:(\\d{1,5})$");
    public static final Pattern ATOM_PATTERN = Pattern.compile("(" + ATOM + ")");
    public static final Pattern ALPHA_PATTERN = Pattern.compile("^[" + ALPHA_CHARS + "]");
    public static final int TOP_LEVEL_DOMAIN_LENGTH_VALUE = 8;
    public static String TOP_LEVEL_DOMAIN_LENGTH = "urlfilter.tld.length";
    private int maxTldLength;

    public UrlValidator(ImmutableConfig conf) {
        maxTldLength = conf.getInt(TOP_LEVEL_DOMAIN_LENGTH, 8);
        if (maxTldLength <= 2)
            maxTldLength = TOP_LEVEL_DOMAIN_LENGTH_VALUE;
    }

    public String filter(String urlString) {
        return isValid(urlString) ? urlString : null;
    }

    /**
     * <p>
     * Checks if a field has a valid url address.
     * </p>
     *
     * @param value The value validation is being performed on. A <code>null</code>
     *              value is considered invalid.
     * @return true if the url is valid.
     */
    @Override
    public boolean isValid(String value) {
        if (value == null) {
            return false;
        }

        Matcher matchUrlPat = URL_PATTERN.matcher(value);
        if (!LEGAL_ASCII_PATTERN.matcher(value).matches()) {
            return false;
        }

        // Check the whole url address structure
        if (!matchUrlPat.matches()) {
            return false;
        }

        if (!isValidScheme(matchUrlPat.group(PARSE_URL_SCHEME))) {
            return false;
        }

        if (!isValidAuthority(matchUrlPat.group(PARSE_URL_AUTHORITY))) {
            return false;
        }

        if (!isValidPath(matchUrlPat.group(PARSE_URL_PATH))) {
            return false;
        }

        if (!isValidQuery(matchUrlPat.group(PARSE_URL_QUERY))) {
            return false;
        }

        return true;
    }

    /**
     * Validate scheme. If schemes[] was initialized to a non null, then only
     * those scheme's are allowed. Note this is slightly different than for the
     * constructor.
     *
     * @param scheme The scheme to validate. A <code>null</code> value is considered
     *               invalid.
     * @return true if valid.
     */
    private boolean isValidScheme(String scheme) {
        if (scheme == null) {
            return false;
        }

        return SCHEME_PATTERN.matcher(scheme).matches();
    }

    /**
     * Returns true if the authority is properly formatted. An authority is the
     * combination of hostname and port. A <code>null</code> authority value is
     * considered invalid.
     *
     * @param authority Authority value to validate.
     * @return true if authority (hostname and port) is valid.
     */
    private boolean isValidAuthority(String authority) {
        if (authority == null) {
            return false;
        }

        Matcher authorityMatcher = AUTHORITY_PATTERN.matcher(authority);
        if (!authorityMatcher.matches()) {
            return false;
        }

        boolean ipV4Address = false;
        boolean hostname = false;
        // check if authority is IP address or hostname
        String hostIP = authorityMatcher.group(PARSE_AUTHORITY_HOST_IP);
        Matcher matchIPV4Pat = IP_V4_DOMAIN_PATTERN.matcher(hostIP);
        ipV4Address = matchIPV4Pat.matches();

        if (ipV4Address) {
            // this is an IP address so check components
            for (int i = 1; i <= 4; i++) {
                String ipSegment = matchIPV4Pat.group(i);
                if (ipSegment == null || ipSegment.length() <= 0) {
                    return false;
                }

                try {
                    if (Integer.parseInt(ipSegment) > 255) {
                        return false;
                    }
                } catch (NumberFormatException e) {
                    return false;
                }

            }
        } else {
            // Domain is hostname name
            hostname = DOMAIN_PATTERN.matcher(hostIP).matches();
        }

        // rightmost hostname will never start with a digit.
        if (hostname) {
            // LOW-TECH FIX FOR VALIDATOR-202
            // TODO: Rewrite to use ArrayList and .add semantics: see VALIDATOR-203
            char[] chars = hostIP.toCharArray();
            int size = 1;
            for (int i = 0; i < chars.length; i++) {
                if (chars[i] == '.') {
                    size++;
                }
            }
            String[] domainSegment = new String[size];
            int segCount = 0;
            int segLen = 0;
            Matcher atomMatcher = ATOM_PATTERN.matcher(hostIP);

            while (atomMatcher.find()) {
                domainSegment[segCount] = atomMatcher.group();
                segLen = domainSegment[segCount].length() + 1;
                hostIP = (segLen >= hostIP.length()) ? "" : hostIP.substring(segLen);
                segCount++;
            }
            String topLevel = domainSegment[segCount - 1];
            if (topLevel.length() < 2 || topLevel.length() > maxTldLength) {
                return false;
            }

            // First letter of top level must be a alpha
            if (!ALPHA_PATTERN.matcher(topLevel.substring(0, 1)).matches()) {
                return false;
            }

            // Make sure there's a host name preceding the authority.
            if (segCount < 2) {
                return false;
            }
        }

        if (!hostname && !ipV4Address) {
            return false;
        }

        String port = authorityMatcher.group(PARSE_AUTHORITY_PORT);
        if (port != null) {
            if (!PORT_PATTERN.matcher(port).matches()) {
                return false;
            }
        }

        String extra = authorityMatcher.group(PARSE_AUTHORITY_EXTRA);
        return isBlankOrNull(extra);
    }

    /**
     * <p>
     * Checks if the field isn't null and length of the field is greater than zero
     * not including whitespace.
     * </p>
     *
     * @param value The value validation is being performed on.
     * @return true if blank or null.
     */
    private boolean isBlankOrNull(String value) {
        return ((value == null) || (value.trim().length() == 0));
    }

    /**
     * Returns true if the path is valid. A <code>null</code> value is considered
     * invalid.
     *
     * @param path Path value to validate.
     * @return true if path is valid.
     */
    private boolean isValidPath(String path) {
        if (path == null) {
            return false;
        }

        if (!PATH_PATTERN.matcher(path).matches()) {
            return false;
        }

        int slash2Count = countToken("//", path);
        int slashCount = countToken("/", path);
        int dot2Count = countToken("..", path);

        return (dot2Count <= 0) || ((slashCount - slash2Count - 1) > dot2Count);
    }

    /**
     * Returns true if the query is null or it's a properly formatted query
     * string.
     *
     * @param query Query value to validate.
     * @return true if query is valid.
     */
    private boolean isValidQuery(String query) {
        if (query == null) {
            return true;
        }

        return QUERY_PATTERN.matcher(query).matches();
    }

    /**
     * Returns the number of times the token appears in the target.
     *
     * @param token  Token value to be counted.
     * @param target Target value to count tokens in.
     * @return the number of tokens.
     */
    private int countToken(String token, String target) {
        int tokenIndex = 0;
        int count = 0;
        while (tokenIndex != -1) {
            tokenIndex = target.indexOf(token, tokenIndex);
            if (tokenIndex > -1) {
                tokenIndex++;
                count++;
            }
        }
        return count;
    }

}